1. 1. Field of the Invention
This invention relates to an apparatus for making light weight insulating cellular concrete by whipping air into a cement-emulsion mixture.
2. Discussion of Prior Art
Heretofore, light weight cellular concrete has commonly been made by whipping a special emulsion into foam and adding this foam to a cement slurry. This is accomplished by mixing cement, water, and sometimes sand or other aggregate, in a concrete mixer. The foam is prepared in a special apparatus in which a foaming agent mixes with air and water forming many air bubbles. When this is added to the cement slurry, the air bubbles trapped in the emulsion remain suspended in the cement mixture. After hardening, the trapped air makes the concrete lighter and more insulating than standard concrete. This process requires a minimum of two tanks, one for mixing the foam and one for the cement slurry. When the foam is injected into the cement slurry, it is difficult to get the foam mixed evenly throughout the cement slurry without defoaming the bubble mixture. When homogeneity is achieved, the mixture is heavier than the product made by a Swedish patented machine (B(21) 8303524-6) described below, and the invention apparatus.
When the concrete from the previous art machine U.S. Pat. No. 4,966,463 is cured, with a density of 38.4 lb/ft.sup.3, the allowable bending stress (flexural strength) is 38.3 psi. Whereas the concrete from the invention apparatus has a density of 18.7 lb/ft.sup.3 and an allowable bending stress of 34.8 psi. This is a 51% reduction in weight with only a 9% reduction in strength.
The above mentioned Swedish machine is a single batch machine which mixes the foam and the cement slurry in the same tank. The system is controlled with a control unit in the form of a micro computer which automatically adds the raw materials at he proper time and in the proper amounts. The complete setup is sufficiently large to require a dedicated truck or a truck and crane to move it from site to site. This Swedish machine is exceptionally expensive due to the automated control unit. This, together with the expense of moving the equipment from site to site, limits its usefulness. In addition, it is not easy to go in and reset the micro computer to make it possible to use a different emulsion.
This machine tends to overfoam the mixture causing the concrete to have less strength. Using the same formula and process for both, the present invention apparatus produced concrete with the compressive strength of 220 psi as compared to 87 psi for the prior art Swedish design. Both tests were done by reliable engineering labs. Lastly, this machine can only make one batch of cellular concrete at a time, restricting its use to small jobs.
One problem that is common to all of the prior art machines is that they can only be used at temperatures above freezing due to the lack of a water preheater.